Firearm ballistic resistive armor dates back to the late 1500s and consisted of metallic armor that was malleable enough to dissipate energy without allowing penetration. The first “soft” ballistic armor known was invented in Korea in the 1860s, which was formed into vests made of 30 folds of cotton. During the early 1880s, silk vests resembling medieval padded jackets were used that consisted of 18 to 30 layers of cloth to stop the relatively slow rounds from black powder handguns.
During World War I, the United States developed several types of body armor, including a chrome nickel steel breastplate and a headpiece that could withstand Lewis Gun bullets at 2,700 feet per second, but was clumsy and heavy at 40 pounds. A scaled waistcoat of overlapping steel scales fixed to a leather lining was also designed. This armor weighed 11 pounds, fit close to the body, and was considered more comfortable. During the late 1920s through the early 1930s, gunmen from criminal gangs in the United States began wearing less-expensive vests made from thick layers of cotton padding and cloth. These early vests could absorb the impact of handgun rounds, such as 0.22, 0.25, S&W 0.32 Long, S&W 0.32, 0.380 ACP, and 0.45 ACP, traveling at slower speeds of up to approximately 1,000 feet per second. To overcome these vests, law enforcement agents, such as those of the FBI, began using the new, more powerful 0.357 Magnum cartridge.
In the early stages of World War II, the United States designed body armor for infantrymen, but most models were heavy and significantly restricted mobility. Additionally, these armor vests were often incompatible with existing equipment. The military diverted its research efforts to developing “flak jackets” for aircraft crews. These flak jackets were made of nylon fabric and capable of stopping flak and shrapnel, but not designed to stop bullets. The Red Army used several types of body armor that consisted of two pressed steel plates that protected the front torso and groin. The plates were 2 mm thick and weighed 7.7 pounds. The United States developed a vest using Doron Plate, a fiberglass-based laminate that was first used by the United States in the Battle of Okinawa in 1945.
During the Korean War, several new vests were produced for the United States military, which made use of fiberglass or aluminum segments woven into a nylon vest, although these vests were not considered very effective. Vietnam War era vests were not simply updated versions of the Korean models but began use of rifle bullet stopping ceramic plates. Vests for aircrews were the first to use ceramic-metal composites, such as boron carbide, silicon carbide, and aluminum oxide, and were capable of stopping rifle fire while giving a very large area of coverage to its wearer.
In the mid-1970s, KEVLAR synthetic fiber was introduced, which was woven into a fabric and layered. KEVLAR is a registered U.S. trademark owned by E. I. du Pont de Nemours and Company (Wilmington, Del.). Immediately, KEVLAR was incorporated into a National Institute of Justice (NIJ) evaluation program to provide lightweight, concealable body armor to ascertain if everyday concealable wearing was possible. It was quickly determined that KEVLAR body armor could be comfortably worn by police daily, and would save lives. In 1975, American Body Armor marketed an all-KEVLAR vest called the K-15, comprised of 15 layers of KEVLAR that also included a 5-inch by 8-inch ballistic steel “Shok Plate” positioned vertically over the heart and was issued U.S. Pat. No. 3,971,072 for this ballistic vest innovation. Similarly sized and positioned “trauma plates” are still used today on the front ballistic panels of most concealable vests, reducing blunt trauma and increasing ballistic protection in the center-mass heart/sternum area.
Since the 1970s, several new fibers and construction methods for bulletproof fabric have been developed besides woven KEVLAR, such as DSM's DYNEEMA, Honeywell's GOLD FLEX and SPECTRA, Teijin's TWARON, Pinnacle Armor's DRAGON SKIN, and Toyobo's ZYLON (now controversial, as new studies report that it degrades rapidly, leaving wearers with significantly less protection than expected). DYNEEMA is a registered U.S. trademark owned by DSM High Performance Fibers B.V. (Netherlands). GOLD FLEX and SPECTRA are registered U.S. trademarks owned by Honeywell International Inc. (Morristown, N.J.). TWARON is a registered U.S. trademark owned by Teijin Aramid B.V. (Netherlands). DRAGON SKIN is a registered U.S. trademark owned by Pinnacle Armor, LLC (Fresno, Calif.). ZYLON is a registered U.S. trademark owned by Toyo Boseki Kabushiki Kaisha, Ta Toyobo Co., Ltd. (Japan). These newer materials are advertised as being lighter, thinner, and more resistant than KEVLAR, although they are much more expensive.
Currently, typical body armor, such as the United States Army's Improved Outer Tactical Vest and United States Marine Corps's Modular Tactical Vest, consists of textile vests augmented with metal (e.g., steel or titanium), ceramic, or polyethylene plates that provide extra protection to vital areas of the body and have become standard for military use. These hard armor plates have proven effective against handguns and a range of rifles. Soft body armor vests consist of layers of very strong fibers that catch and deform soft bullets and spread their force over a larger portion of the vest fiber. In the process, the vest absorbs the energy from the bullet, bringing it to a stop before it can penetrate the vest. A deformable handgun bullet mushrooms into a dished plate on impact with a well-designed textile vest. Some layers of the vest may be penetrated, but as the bullet deforms, the energy is absorbed by a larger and larger fiber area. While a vest can prevent bullet penetration, the vest and wearer still absorb the bullet's energy. Even without penetration, modern pistol bullets contain enough energy to cause blunt force trauma under the impact point. Vest specifications include both penetration resistance requirements and limits on the amount of impact energy that is delivered to the body.
Vests designed for bullets offer little protection against stabbing knife blows, arrows, ice picks, and bullets manufactured of non-deformable materials (i.e. steel core instead of lead). As the force is concentrated in a relatively small area with bladed weapons and non-deformable rounds, they can push and cut through the fiber layers of most bullet-resistant fabrics. Specially-designed vests which protect against bladed weapons and sharp objects are often used in vests for corrections officers and other law enforcement officers. Some materials, such as coated and laminated para-aramid textile, offer considerable protection against bladed weapons and slash attacks. More advanced protection for knives makes use of metallic vest components.
Rifle resistant armor is predominantly of two basic types: ceramic plate-based systems, and hard fiber-based laminate systems. Many rifle armor components contain both hard ceramic components and laminated textile materials used together. Various ceramic materials are in use; however, aluminum oxide, boron carbide, and silicon carbide are the most common. The fibers used in these systems are the same as found in soft textile armor. However, for rifle protection, high pressure lamination of ultra-high molecular weight polyethylene with a KRATON matrix is the most common. KRATON is a registered U.S. trademark owned by Kraton Polymers (Houston, Tex.). The Small Arms Protective Insert (SAPI) and the enhanced SAPI plate for the U.S. Department of Defense (DoD) Interceptor Body Armor generally has this form. Because of the use of ceramic plates for rifle protection, these vests are five to eight times heavier on an area basis than vests for handgun protection. The weight and stiffness of rifle armor is a major technical challenge. The density, hardness, and impact toughness are among the materials properties that are balanced to design these systems. While ceramic materials have some outstanding properties for ballistics, they are not strong under tensile loads. Failure of ceramic plates by cracking must also be controlled. For this reason, many ceramic rifle plates are a composite. The strike face is ceramic with the backface formed of laminated fiber and resin materials. The hardness of the ceramic prevents the penetration of the bullet, while the tensile strength of the fiber backing helps prevent tensile failure.
For defense against more substantial threats, such as from higher caliber weapons, cannons, and other larger projectiles, armor has predominantly consisted of dense metallic and ceramic materials that resist impact loads through sheer density of the impact surface. For these applications, heavy armor panels are applied parasitically, in that they are externally applied to the surface area to be protected. These heavy armor applications possess the key disadvantage of significant added weight, and can also create additional collateral damage if penetrated and compromised by becoming projectiles themselves.
In addition to static armor systems, there is a type of armor known as “Reactive Armor” that reacts in some way to the impact of a weapon to reduce the damage done to the object being protected. It is most effective in protecting against shaped charges and long rod penetrators. The most common type is Explosive Reactive Armor (ERA), which typically consists of a sheet or slab of high explosive sandwiched between two plates, typically metal, called the reactive or dynamic elements. On attack by a penetrating weapon, the explosive detonates, forcibly driving the metal plates apart to damage the penetrator. Variants include Self-Limiting Explosive Reactive Armor (SLERA), Non-Energetic Reactive Armor (NERA), Non-Explosive Reactive Armor (NxRA), and Electric Reactive Armor. Unlike ERA and SLERA, NERA and NxRA modules can withstand multiple hits, but a second hit in exactly the same location will still penetrate.
National Institute of Justice (NIJ) Standard-0101.06 and NIJ Standard-0108.01 classifies body armor and vehicle armor into seven different threat levels consisting of, in order from lowest to highest level of protection: Type I, Type IIA, Type II, Type IIIA, Type III, Type IV, and Special. Each of these armor protection levels is described generally below.
Type I (22 LR; 380 ACP) armor protects against .22 caliber Long Rifle Lead Round Nose (LR LRN) bullets, with nominal masses of 2.6 g (40 gr) impacting at a minimum velocity of 320 m/s (1050 ft/s) or less, and 380 ACP Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 6.2 g (95 gr) impacting at a minimum velocity of 312 m/s (1025 ft/s) or less.
Type IIA (9 mm; 40 S&W) armor protects against 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 8.0 g (124 gr) impacting at a minimum velocity of 332 m/s (1090 ft/s) or less, and 40 S&W caliber Full Metal Jacketed (FMJ) bullets, with nominal masses of 11.7 g (180 gr) impacting at a minimum velocity of 312 m/s (1025 ft/s) or less. It also provides protection against the threats described above with respect to Type I armor.
Type II (9 mm; 357 Magnum) armor protects against 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 8.0 g (124 gr) impacting at a minimum velocity of 358 m/s (1175 ft/s) or less, and 357 Magnum Jacketed Soft Point (JSP) bullets, with nominal masses of 10.2 g (158 gr) impacting at a minimum velocity of 427 m/s (1400 ft/s) or less. It also provides protection against the threats described above with respect to Type I and Type IIA armor.
Type IIIA (High Velocity 9 mm; 44 Magnum) armor protects against 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 8.0 g (124 gr) impacting at a minimum velocity of 427 m/s (1400 ft/s) or less, and 44 Magnum Semi Jacketed Hollow Point (SJHP) bullets, with nominal masses of 15.6 g (240 gr) impacting at a minimum velocity of 427 m/s (1400 ft/s) or less. It also provides protection against most handgun threats, as well as the threats described above with respect to Type I, Type IIA, and Type II armor.
Type III (Rifles) armor protects against 7.62 mm Full Metal Jacketed (FMJ) bullets (U.S. Military designation M80), with nominal masses of 9.6 g (148 gr) impacting at a minimum velocity of 838 m/s (2750 ft/s) or less. It also provides protection against the threats described above with respect to Type I, Type IIA, Type II, and Type IIIA armor.
Type IV (Armor Piercing Rifle) armor protects against .30 caliber armor piercing (AP) bullets (U.S. Military designation M2 AP), with nominal masses of 10.8 g (166 gr) impacting at a minimum velocity of 869 m/s (2850 ft/s) or less. It also provides at least single hit protection against the threats described above with respect to Type I, Type IIA, Type II, Type IIIA, and Type III armor.
Special Type armor protects against threat levels other than one of the above standard types. A purchaser having a special requirement for a level of protection other than one of the above standard types and threat levels should specify the exact test round(s) and minimum reference impact velocities to be used, and indicate that this standard shall govern in all other aspects.
In addition to NIJ standards, military ballistic protection requirements are defined in MIL-STD-662F which provides general guidelines for procedures, equipment, physical conditions, and terminology for determining the ballistic resistance of metallic, nonmetallic, and composite armor against small arms projectiles. Other standards include, but are not limited to, MIL-STD-2105C, Hazard Assessment Tests for Non-nuclear Munitions; MIL-PRF-46103E, Performance Specification Armor Lightweight Composite; NATO AEP-55 STANAG 4569, Protection Levels for Occupants of Logistic and Light Armor Vehicles; and MIL-STD-810G, DOD Test Method Standard Environmental Engineering Considerations and Laboratory Tests.
Testing protocols provide that textile armor is tested for both penetration resistance by bullets and for the impact energy transmitted to the wearer. The “backface signature” or transmitted impact energy is measured by shooting armor mounted in front of a backing material, typically sculpture modeling oil-clay. The clay is used at a controlled temperature and verified for impact flow before testing. After the armor is impacted with the test bullet, the vest is removed from the clay and the depth of the indentation in the clay is measured.
The backface signature allowed by different test standards can be difficult to compare. Both the clay materials and the bullets used for the test are not common. However, in general, the U.K., German, and other European standards allow 20-25 mm of backface signature while the U.S.-NIJ standards allow for 44 mm, which can potentially cause internal injury. The allowable backface signature for body armor has been controversial since its introduction in the first NIJ test standard, and the debate as to the relative importance of penetration-resistance versus backface signature continues in the medical and testing communities.
In general, a vest's textile material temporarily degrades when wet. Neutral water at room temperature does not affect para-aramid or ultra-high molecular weight polyethylene (UHMWPE), but acidic, basic, and some other solutions can permanently reduce para-aramid fiber tensile strength. Because of this, the major test standards call for wet testing of textile armor. Mechanisms for this wet loss of performance are not known. Vests tested after ISO-type water immersion tend to have heat-sealed enclosures and those tested under NIJ-type water spray methods tend to have water-resistant enclosures.
Some existing armor systems encase the armor solution using methods ranging from simply applying coatings as a vapor barrier to fiberglass wrapping to serve as environmental protection and abrasion resistance, but not for the express purpose of enhancing the structural integrity of the armor system. Some of these systems on the commercial market include, but are not limited to, the following products. Tencate Advanced Armor, also known as (TCAA), uses a fiberglass and S-Glass matrix to form an outer encasement to provide an abrasive resistant and hardened enclosure for the armor system. Texstars ARMORsmith armor uses an aramid fiber “spall liner” as a form of encapsulation. This layer is designed to reduce or contain the fragments of the inner materials upon a ballistic impact. Another such system is manufactured by ArmorStruxx and incorporates the use of composite armor with an aluminum cladding on the exterior to provide a complete system for building larger structures. Safari Land uses a Cordura nylon to encapsulate body armor panels into a protected panel system that is impervious to water and bio-hazards, and provides a degree of abrasion and penetration resistance.